This invention relates to optical fiber arrays and, in particular, to optical fiber arrays presenting polished fiber ends angled for reduced return loss. It also includes methods for making such arrays.
One of the major advances in communications in recent years has been the increased use of optical fiber systems for carrying large quantities of information with low distortion and low cost over great distances. Optical systems are also very promising for computing and for switching because of the inherently high speeds at which they operate. For these reasons, considerable work has been expended to develop techniques for switching light beams directly, without converting the light to electrical energy. The use of such devices will depend to a great extent on the facility with which they can be made.
A free-space photonics switch which takes light from the end of a bundle of optical fibers, performs desired switching functions, and then projects the light into the end of a second bundle of optical fibers is described in the paper, xe2x80x9cAll-Optical Implementation of a 3-D Crossover Switching Network,xe2x80x9d by T. J. Cloonan et al. IEEE Photonics Technology Letters, Vol. 2, No. 6, Jun. 1990, pp. 438-440. The optical fiber ends of each bundle form a matrix array, which must be accurately registered with the other apparatus.
Conventional fiber arrays for free-space optical switching use nxc3x97n arrays of parallel fibers with the fiber ends presented on an array faceplate perpendicular to the fibers. The faceplate is typically made from silicon and includes an array of precision holes for insertion and alignment of the fibers, which are mounted in the faceplate with epoxy. The ends of the mounted fibers are polished against the faceplate surface. The fabrication of such arrays is described in greater detail in U.S. Pat. No. 5,135,590 issued to Basavanhally et al. on Aug. 4, 1992 and U.S. Pat. No. 5,185,846 issued to Basavanhally et al. on Feb. 9, 1993, both of which are incorporated herein by reference.
A difficulty with these conventional arrays is return loss. Light from a fiber incident on the flat fiber end reflects back into the fiber toward the laser source with deleterious consequences. An antireflection coating may be placed on the flat ends to reduce the return loss, but such coatings have only reduced return loss, not eliminated it. Precision mounted fiber arrays with further reduced return loss would be highly desirable.
In accordance with the invention, an optical fiber array comprises a substrate providing a planar array of optical fibers. The optical fibers are parallel to the array axis, but the fiber ends present smooth, polished surfaces angled from the array axis to minimize return loss of light directed along the axis. Three embodiments are described. The first is a series of 1xc3x97n strip arrays each mounted at an angle to the array axis to form a saw tooth configuration faceplate. The holes in each strip are also angled to compensate for the angled mount. A second embodiment uses an angled planar faceplate having tapered holes. A third embodiment uses an angled faceplate planar with double-tapered holes to obtain the angled end surfaces. In each embodiment, the fiber ends are substantially coplanar with the faceplate surface but the ends are angled with respect to the array axis.